Flavocytochrome domain interactions

FIGURE 7. Stereo diagram of one subunit of flavocytochrome b. Only residues ln486 are shown, the remainder being involved in intermolecular interactions. The flavin-binding domain is at the top and the cytochrome domain is at the bottom. The flavin and heme groups are shown as skeletal models. 

The characterisation of the complexation between flavocytochrome b2 and cytochrome c has been the subject of many studies (see for example Short et al., 1998 Daff et al., 1996b and CapeillEre-Blandin, 1995). Work on the anomala flavocytochrome b2, for which there is no crystal structure, led to the conclusions that the cytochrome c binding site involved both the flavodehydrogenase and cytochrome domains (CapeillEre-Blandin and Albani, 1987) and that the complex was stabilised by electrostatic interactions (CapeillEre-Blandin, 1982). It is clear that similar conclusions hold true for the S. cerevisiae enzyme (Daff et al., 1996b) for which the crystal... 

NMR at 400 MHz has been used to probe the mobility of the cytochrome domain within the holoenzyme (84). The linewidths of heme resonances downfield of 4-12 ppm and upheld of -4 ppm have been compared for the holoenzyme and the cytochrome 62 core and indicate that the cytochrome domains of the holoenzyme are markedly mobile (84). NMR has also been used to investigate the nature of the interaction between flavocytochrome 62 and cytochrome c (85,86) with the ultimate aim of defining the binding site on flavocytochrome 62 used by its physiological partner. The extensive NMR studies on the interaction between cytochrome 65 and cytochrome c (87,88) provide a useful background to the work with cytochrome 62 ... 

Addition of cytochrome hi core to a solution of TNS does not modify the fluorescence of the probe. However, upon addition of the cytochrome to a solution of FDH-TNS complex, an increase in TNS fluorescence was observed, as the result of an increase in the affinity between the probe and the flavoprotein (A.ex, 320 nm) (Albani, 1993). X-ray diffraction studies have indicated that FMN is buried in the flavin-binding domain of flavocytochrome hi (Zia et al. 1990), and fluorescence studies have shown that binding of TNS to the FDH does not induce any release of the flavin from its binding site (Albani, 1993). Titration of a constant concentration of FDH-TNS complex with cytochrome hi core yields a sigmoidal curve for the TNS intensity increase (Fig. 4.18) (Albani, 1997). Thus, interaction between cytochrome hi core and FDH is cooperative. 

Noble MA, Girvan HM, Smith SJ, Smith WE, Mu-rataliev M, Guzov VM, Feyereisen R, Munro AW (2007) Analysis of the interactions of cytochrome bj with flavocytochrome P450 BM3 and its domains. Drug Metab Rev 39 599-617... 

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